Exhaust heat recovery system having a working fluid circuit and method for operating such an exhaust heat recovery system

ABSTRACT

The invention relates to an exhaust heat recovery system having a working fluid circuit (1) carrying a working fluid, having a heat exchanger (2) which is connected in an exhaust line (3) of an internal combustion engine (5) and which is a part of the working fluid circuit (1) together with at least one expansion machine (11), a condenser (12), and a fluid pump (15). The aim of the invention is to provide an exhaust heat recovery system, which is improved with respect to known systems. This is achieved in that the exhaust heat recovery system has a device (27) for avoiding damage to the expansion machine (11) that is caused by liquid components of the working fluid. The device (11) is, for example, a container (21), a calming container (28, 28a), a line section (36) or a filter (26), or the device (11) has at least one such component.

BACKGROUND OF THE INVENTION

The present invention concerns an exhaust heat recovery system having a working fluid circuit carrying a working fluid, comprising at least one heat exchanger which is connected in an exhaust gas line of an internal combustion engine and which is a part of the working fluid circuit together with at least one expansion machine, a condenser and at least one fluid pump. The invention also concerns a method for operating such a working fluid circuit.

Such an exhaust heat recovery system is disclosed in DE 10 2013 211 875. This exhaust heat recovery system comprises a working fluid circuit with two heat exchangers, wherein a first heat exchanger is connected in an exhaust gas line of the internal combustion engine, and a second heat exchanger is connected in an exhaust gas recirculation line of the internal combustion engine. The working fluid circuit furthermore comprises an expansion machine, a condenser and a fluid pump, wherein downstream of the fluid pump, the working fluid circuit is divided into two fluid branches which lead to the first heat exchanger and second heat exchanger respectively. At the start of the fluid branches, a distribution valve is inserted which sets the quantity of working fluid supplied to the heat exchangers. In the case of an internal combustion engine installed in a vehicle, the resulting exhaust heat recovery system is normally fitted at least partially in an engine bay of the vehicle receiving the internal combustion engine.

SUMMARY OF THE INVENTION

The invention is based on the object of providing an exhaust heat recovery system which is improved in relation to known systems.

This object is achieved in that the exhaust heat recovery system comprises a device for avoiding damage to the expansion machine caused by liquid components of the working fluid. The method for operating the exhaust heat recovery system provides that by means of a device, liquid components are separated from the working fluid and/or rendered harmless so as to exclude damage to the expansion machine from liquid components. This embodiment and this method are based on the knowledge that, in particular when the expansion machine is configured as a turbomachine with a turbine impeller having turbine blades, the quality of the vaporous working fluid supplied to the expansion machine is extremely important. This is because a turbomachine is operated at very high rotation speeds, which leads to very high relative speeds at the turbine blades of the turbomachine. If the turbomachine is not operated with a monophasic gaseous working fluid (as dry vapor), but rather with a vaporous working fluid which carries with it unvaporized working fluid in the liquid phase (liquid components in the working fluid, for example in the form of liquid droplets) in the form of wet vapor, erosion occurs at the turbine blades because of collision processes. Furthermore, the exhaust heat recovery system often contains a temperature sensor, configured for example as a thermometer, directly upstream of the turbomachine. If the thermosensor is hit by a liquid droplet or if the liquid droplet is deposited on the thermosensor, an actual measurement value is falsified, which has a disadvantageous effect on the system regulation. Since the presence of wet vapor (gaseous vapor with liquid components) in the working fluid cannot or should not be prevented because of the operating strategy, for example in order to increase the efficiency, the turbomachine must either be tolerant of wet vapor or the liquid components must be conducted past the expansion machine according to the invention, or the working fluid must be cleaned of the liquid components upstream of the turbomachine. This is achieved by the initially freely configured device.

In a refinement of the invention, the device is arranged in the working fluid circuit between an outlet from the at least one heat exchanger and the expansion machine. Here, the device is normally arranged directly before the inlet of the working fluid circuit into the expansion machine. This ensures that only the working fluid supplied to the expansion machine actually flows through the device. It is however also conceivable to place the device after a first heat exchanger and before merging with the second heat exchanger, insofar as this “safely” generates superheated vapor i.e. monophasic gaseous working fluid.

In a further embodiment of the invention, the device is a device for separating the liquid components from the working fluid. The device or separating device is a container, a calming container or a line portion of the working fluid circuit, or comprises such a component.

In a further embodiment, the device, in particular the container or the line portion, comprises a guide device, in particular at least one guide plate. This guide device sets the working fluid, which preferably flows into the container axially and contains liquid components, into a rotational motion, whereby the liquid components, in particular in the form of liquid droplets, are flung onto a peripheral wall of the container or line portion where they adhere. From there, the liquid components may either be discharged to the outside of the device or rendered harmless, for example by vaporization. A combination of both options is also possible.

In a further embodiment of the invention, the device in the form of the container, the calming container and/or the line portion, has a rotation device moving the liquid components onto a peripheral wall. This rotation device may in a general embodiment be configured arbitrarily, wherein the rotation device preferably is at least one tangential inflow inlet which is connected to the working fluid circuit. The working fluid comprising the liquid components passes through the tangential inflow inlet into the device and is set in rotation inside the device. This rotation causes the (heavy) liquid components to be separated from the working fluid under the effect of centrifugal force, and they are then for example discharged from the device through a liquid outlet provided in a further embodiment, and supplied back to the working fluid circuit for example downstream of the expansion machine. A further embodiment provides that the liquid components are continuously or discontinuously vaporized in the device. The working fluid free from liquid components leaves the device in the form of dry vapor Td, for example via an axial outflow outlet, and is supplied to the expansion machine.

In a refinement of the invention, the device is a filter or comprises a filter. The filter may for example be a membrane filter or a sinter filter in which the liquid components of the working fluid are separated out (and either supplied to the working fluid circuit via a liquid outlet, for example downstream of the expansion machine, or converted into dry vapor via a heating device). The filter may be configured such that it has a sufficiently large liquid storage capacity for operating phases with wet vapor, wherein the collected liquid components are vaporized via operating phases with superheated vapor and hence the filter is regenerated. The filter may however also be a chemical filter, for example from the substance group of zeolites.

In a refinement of the invention, the device is a calming container. The calming container is in principle configured such that the flow speed is reduced so the liquid components have sufficient time to vaporize. If the liquid components do not vaporize but are deposited, for example because of the construction, a return via said liquid outlet is possible, where applicable with the inclusion of a choke in the low-pressure part of the exhaust heat recovery system. Also, in the region of the calming container or device in general in which the liquid components are precipitated, a heating system may be provided which reliably vaporizes the liquid components.

In a refinement of the invention, the device comprises a magnet which generates a strong magnetic field which in turn leads to a charge separation at the liquid components, i.e. the liquid droplets, and hence allows deflection. The liquid components may again be deposited on the walls of the device and discharged or converted as described above.

In brief, according to the invention, the following advantages are achieved:

-   -   the working fluid is treated economically so that the liquid         components carried constitute no danger to the expansion         machine,     -   the exhaust heat recovery system is more robust,     -   the exhaust heat recovery system may be operated for longer         periods since the expansion machine need be bypassed more rarely         via a bypass line due to liquid components present in the         working fluid,     -   the use of an economic thermosensor is possible,     -   the system regulation becomes simpler due to the increased         security against wet vapor,     -   the increased robustness of the system leads to a higher energy         yield and a higher overall efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous embodiments of the invention are given in the description of the drawings in which an exemplary embodiment shown in the figures is described in more detail.

The drawings show:

FIG. 1 a circuit diagram of an exhaust heat recovery system configured according to the invention with a working fluid circuit and a device for avoiding damage to an expansion machine caused by liquid components of the working fluid,

FIG. 2 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a first embodiment,

FIG. 3 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 4 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 5 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 6 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 7 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 8 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 9 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment,

FIG. 10 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment, and

FIG. 11 a detail view of a device for avoiding damage to an expansion machine caused by liquid components of the working fluid in a further embodiment.

DETAILED DESCRIPTION

The exhaust heat recovery system shown diagrammatically in FIG. 1 has a working fluid circuit 1 with a first heat exchanger 2 a and a second heat exchanger 2 b, wherein in principle only a single heat exchanger or also more than two heat exchangers may be part of the exhaust heat recovery system. The heat exchangers 2 a, 2 b are configured as or function as evaporators, and on an internal combustion engine 5, are adapted for recovery of the waste heat generated in operation of the internal combustion engine 5. An exhaust gas stream 4 from the internal combustion engine 5, which is guided in an exhaust gas line 3 of the internal combustion engine and forms a waste heat stream, flows through the first heat exchanger 2 a. In addition to the first heat exchanger 2 a, the second heat exchanger 2 b is installed in a line in the form of an exhaust gas recirculation line 6 or other heat transfer line. Via the exhaust gas recirculation line 6, a partial quantity of exhaust gas is taken from the exhaust gas stream 4 and supplied under control via an exhaust gas recirculation valve 7 to an intake system 8 of the internal combustion engine 5. The intake system 8 may preferably be configured as a charge air conduction system. The two heat exchangers 2 a, 2 b may in some cases be able to be bypassed via heat exchanger bypass lines (not shown) in certain operating states of the internal combustion engine 5 of the vehicle in which the internal combustion engine 5 is preferably installed. When the internal combustion engine 5 is installed in the vehicle, the internal combustion engine 5 and the exhaust heat recovery system, together with the working fluid circuit 1 and the components mentioned above or to be described below, are preferably installed at least partially in an engine bay of the vehicle.

During operation, fuel and combustion air supplied to the internal combustion engine 5 and combusted in combustion chambers of the internal combustion engine 5, generating working power and hot exhaust gas which forms the exhaust gas stream 4 in operation of the internal combustion engine 5. The exhaust gas stream 4 is discharged finally into the environment through the exhaust gas line 3, from which the exhaust gas recirculation line 6 branches. Upstream and/or downstream of the first heat exchanger 2 a, exhaust silencers 9 and devices 10 for aftertreatment of the exhaust gas, in the form for example of a catalytic converter and/or a filter, may be installed in any order in the exhaust gas line 3. The internal combustion engine 5 is for example a self-igniting internal combustion engine which is operated with diesel fuel. The diesel fuel is injected into the combustion chambers for example by means of a common rail injection system. The internal combustion engine may also be an externally ignited, petrol-operated internal combustion engine which may also have a common rail injection system.

The first heat exchanger 2 a and the second heat exchanger 2 b are, as already stated, themselves part of the working fluid circuit 1, which as well as the heat exchangers 2 a, 2 b, comprises an expansion machine 11, a condenser 12, in some cases a condenser pump 13, an expansion tank 14 and one or two fluid pumps 15 a, 15 b. The fluid pump 15 a is connected fluidically via a first supply line 16 a to the first heat exchanger 2 a, and the second fluid pump 15 b is connected fluidically via a second supply line 16 b to the second heat exchanger 2 b. The fluid pumps 15 a, 15 b may be independent pumps or for example be configured in the form of a double-stroke vane pump. For example, a double-stroke vane pump may be set so that, for a constant or adjustable total delivery quantity of the working fluid, a distribution of the delivery quantity to the first heat exchanger 2 a and to the second heat exchanger 2 b can be set so as to increase and correspondingly decrease between 0% and 100%. The total delivery quantity may be set for example by changing the rotation speed of the fluid pumps 15 a, 15 b. As indicated above, also merely a single fluid pump 15 may be present, wherein then control valves are fitted in the first supply line 16 a and in the second supply line 16 b for setting the delivery quantity distribution. If only a single heat exchanger is present, evidently the delivery quantity distribution described above is not required.

The expansion machine 11 is preferably a turbomachine having at least one turbine impeller with turbine blades, normally with a reduction gear mechanism connected downstream thereof in order to reduce the high turbine rotation speeds and adapt these to the rotation speeds of a downstream working machine or other consumer.

In operation of the exhaust heat recovery system, fluid suitable for a Rankine process, e.g. ethanol, cyclopentane, or a refrigerant, is brought to a high pressure by the fluid pumps 15 a, 15 b and supplied to the heat exchangers 2 a, 2 b. The fluid is heated in the heat exchangers 2 a, 2 b and transformed into the vaporous state under high pressure. The resulting vapor is supplied to the expansion machine 11 and drives this under expansion of the working fluid. In order to be able to conduct the working fluid circuit 1 past the expansion machine 11, a bypass line 17 with a bypass valve 18 may be provided, via which the expansion machine 11 can be bypassed. To prevent the expansion machine and in particular the turbine impeller from being exposed to liquid components which may be contained in the working fluid even in the vaporous state or be present in a critical constellation, a device 27 is installed in the working fluid circuit 1 before the inlet to the expansion machine 11. The device 27 retains the liquid components and discharges these appropriately, converts them or otherwise renders them harmless. In this way, the turbine impeller or other parts of the expansion machine 11 are protected from liquid components for example in the form of liquid droplets 25 (FIG. 2). The device may also have two inlets, as will be explained below. This is the case for example if the outlet lines from the heat exchangers 2 a, 2 b are guided right to the device 27 and the bypass line 17 branches off the outlet lines at a suitable point before this. This would mean that two bypasses may be required. It is also conceivable, at least for some embodiments (not for the filter variants), to place the device 27 before the bypass. It is also conceivable to integrate the bypass, i.e. the bypass line 17, in the device 27.

The working fluid supplied to the expansion machine 11 expands here, generating mechanical shaft work which is dissipated via an outlet shaft 19. The outlet shaft 19 may for example be coupled to a generator for generating electrical power. Then the cold vapor is condensed in the condenser 12 and finally supplied back to the fluid pumps 15 a, 15 b. The expansion tank 14 may be connected in the connecting line between the condenser 12 and the double-stroke vane pump 16. As well as the components described above, any further components, such as in particular sensors for determining temperatures and pressures, may be present in various portions of the working fluid circuit 1. Furthermore, a control unit 20 is provided for controlling the exhaust heat recovery system.

FIG. 2 shows a device 27, for example in the form of a container 21, which is installed in the working fluid circuit 1 at the point shown in FIG. 1 directly before the expansion machine 11. For this, the pipeline system forming the working fluid circuit 1 may have flange connections which can be connected to the container 21, for example by screwing. It is also possible to arrange the device 27 precisely in the region of the point at which the expansion machine 11 is connected to the pipeline system. The device 27 may also be integrated directly in the pipeline system as a line portion, wherein then the container 21 is omitted. The container 21 has an axial inflow inlet 22 through which the working fluid with liquid components enters the container 21. Guide devices in the form of guide plates 24 are arranged in the container 21 and set the incoming working fluid into the rotation R depicted. This rotation R separates liquid components, for example in the form of fluid droplets 25, out of the working fluid which leaves the container 21 as “pure” dry vapor via an outflow outlet 23 in the direction of the expansion machine 11. The liquid components in the form of liquid droplets 25 may then, as will be explained partially below, either be supplied for example via a liquid outlet to the working fluid circuit 1, for example after the expansion machine 11, or be converted into dry vapor via a heating device, or be vaporized in operating phases with superheated vapor.

FIG. 3 shows a device 27 in the form of a container 21 which has a tangential inflow inlet 22 a. The working fluid comprising the liquid components enters the container 21 through the tangential inflow inlet 22 a and is thereby set in rotation R. Also the fluid droplets 27 are separated thereby and the working fluid leaves the container 21 as dry vapor through the axial outflow outlet 23. In addition, guide plates 24 may also be present in this container 21.

In the exemplary embodiment shown in FIG. 4, in contrast to the exemplary embodiment in FIG. 3, two tangential inflow inlets 22 a are provided on the container 21, and for example are connected to the outlet lines of the heat exchangers 2 a, 2 b through which the working fluid flows into the container 21. Evidently, it is also possible to provide more than two tangential inflow inlets 22 a on the container 21.

FIG. 5 shows diagrammatically a device 27 configured as a filter 26 in the form of a sinter filter, through which the working fluid comprising the liquid components leaves the sinter filter 26 as dry vapor Td. Merely for illustration, wet vapor Nd and dry vapor Td are shown as separate strands before the filter 26 but evidently enter the filter 26 as one strand. The two strands may also however represent the lines from the two heat exchangers 2 a, 2 b, which therefore conduct working fluid in the form of wet vapor Nd and dry vapor Td.

The exemplary embodiment shown in FIG. 6 shows a filter 26 in the form of a chemical filter, for example a zeolite, which stores the liquid components. The filter 26 is regenerated when working fluid in the form of (exclusively) superheated vapor is supplied to the chemical filter and converts the liquid components into dry vapor Td.

The exemplary embodiment in FIG. 7 shows a device 27 configured as a calming container 28 in which a baffle plate 29 is inserted. The baffle plate 29 is arranged such that the incoming working fluid hits the baffle plate 29 and the liquid components are thereby separated out and settle on the floor of the calming container 28 as liquid droplets 25. Outside the calming container 28, a heater 30 may be provided below the floor which vaporizes the liquid droplets 25 again.

The exemplary embodiment in FIG. 8 shows a device 27 in the form of a calming container 28 a which has a liquid outlet 31 at a geodetically low point. The liquid outlet 31 is connected to a discharge line 32 in which a choke 33 may be inserted or which is itself formed as a choke. The discharge line 32 is connected to the working fluid circuit 1 in the region downstream of the condenser 12. Liquid droplets 25 are returned to the working fluid circuit 1 through the discharge line 32. The discharge line 32 may however also open into the working fluid circuit 1 downstream of the expansion machine 11 and upstream of the condenser 12. This may be useful for example under specific spatial circumstances.

The exemplary embodiment in FIG. 9 has a similar design to FIG. 8, wherein here a membrane 34, which is impermeable to the liquid components and is connected to the outflow outlet 23 a, is fitted in the calming container 28 a. The liquid droplets 25 again settle on the floor and, as explained above, are returned to the working fluid circuit 1.

The exemplary embodiment in FIG. 10 has nozzles 35 through which the working fluid, in the form of wet vapor Nd containing the liquid droplets 25, is injected into a device 27, for example in the form of a container 21. The liquid components in the form of liquid droplets 25 a are atomized by the nozzles 25 so that they can be conducted through the expansion machine 11 together with the dry vapor Td without causing damage.

The exemplary embodiment in FIG. 11 shows a device 27 in the form of a line portion 36, on the outside of which a magnet 37 is arranged, for example in the form of an electromagnet 37 a and or a permanent magnet 37 b, which separates the electrically charged fluid droplets 25 out of the through-flowing working fluid. Preferably, the strong electromagnetic field first causes a charge separation and then the fluid droplets 25 are attracted to the wall by the permanent magnet 37 b.

Finally, it is pointed out that any partial features of the invention described above may be combined with any or all other such features where technically useful. 

1. An exhaust heat recovery system having a working fluid circuit (1) carrying a working fluid, comprising at least one heat exchanger (2) which is connected in an exhaust gas line (3) of an internal combustion engine (5) and which is a part of the working fluid circuit (1) together with at least one expansion machine (11), a condenser (12), and at least one fluid pump (15), characterized in that the exhaust heat recovery system comprises a device (27) for avoiding damage to the expansion machine (11) caused by liquid components of the working fluid.
 2. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) is arranged in the working fluid circuit between an outlet from the heat exchanger (2) and the expansion machine (11).
 3. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) is configured to separate the liquid components from the working fluid.
 4. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) comprises a guide device.
 5. The exhaust heat recovery system as claimed in claim 3, characterized in that the device (27) comprises at least one tangential inflow inlet (22, 22 a).
 6. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) is a filter (26).
 7. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) comprises a heater (37).
 8. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) comprises a liquid outlet (31).
 9. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) comprises a nozzle (35).
 10. The exhaust heat recovery system as claimed in claim 1, characterized in that the device (27) comprises a magnet (37).
 11. A method for operating an exhaust heat recovery system having a working fluid circuit (1) carrying a working fluid, the exhaust heat recovery system comprising at least one heat exchanger (2) which is connected in an exhaust gas line (3) of an internal combustion engine (5) and which is a part of the working fluid circuit (1) together with at least one expansion machine (11), a condenser (12), and at least one fluid pump (15), of the method comprising using a device (27) to separate liquid components from the working fluid and/or to render harmless the liquid components so as to exclude damage to the expansion machine (11) from the liquid components.
 12. The exhaust heat recovery system as claimed in claim 3, characterized in that the device (27) is a container (21).
 13. The exhaust heat recovery system as claimed in claim 12, characterized in that the container (21) has therein a guide plate (24).
 14. The exhaust heat recovery system as claimed in claim 13, characterized in that the container (21) comprises at least one tangential inflow inlet (22, 22 a).
 15. The exhaust heat recovery system as claimed in claim 3, characterized in that the device (27) is a calming container (28, 28 a).
 16. The exhaust heat recovery system as claimed in claim 15, characterized in that the calming container (28, 28 a) has therein a baffle plate (29).
 17. The exhaust heat recovery system as claimed in claim 16, characterized in that the calming container (28, 28 a) comprises at least one tangential inflow inlet (22, 22 a).
 18. The exhaust heat recovery system as claimed in claim 3, characterized in that the device (27) is a line portion (36) of the working fluid circuit (1).
 19. The exhaust heat recovery system as claimed in claim 19, characterized in that a magnet (37) is arranged on the outside of the line portion (36) such that the magnet (37) separates electrically charged fluid droplets (25) out of the working fluid flowing through the line portion (36).
 20. The exhaust heat recovery system as claimed in claim 18, characterized in that the line portion (36) comprises at least one tangential inflow inlet (22, 22 a). 